**1. Introduction**

#### **1.1 Definition**

Since the beginning of agriculture, farmers had to compete with the harmful organisms called "Pests". These organisms are not only responsible for potential loss of revenue due to heavy crop damage and reduced food supplies but also significantly damage the machinery, equipment and property as well. They are prevented, destroyed, repelled or mitigated using different types of pesticides such as insecticides, herbicides, rodenticides and fungicides. Such chemical control methods are neither always economical nor effective and are generally associated with unwanted health, safety and environmental risks.

Therefore, in the recent decades, elevated awareness on the impacts of pesticide use on the human health and environment has fostered to decrease the reliance on chemical controls. Furthermore, the development of pesticide resistance is also indicative for the need of change for pests management with emphasis on the human health and environment. In this regard, biologically based technologies


#### **Table 1.**

*Different types of biological control agents.*

could be more convectional to solve the urgent needs in pest management. Biological control or biocontrol is particularly the use of animals, fungi, or other microbes to feed upon, parasitize or interfere with a targeted pest species. When the chemical pesticides were not appropriate for controlling the specific pest, the use of biological control came as a practical solution to the pest problem. The biological control method is innovative and sustainable way to control pests. This method leaves no chemical residues and has no harmful impact on the humans or other organisms. If the method is successfully implemented following introduction, it may provide a permanent control with favaourable cost–benefit ratio. A commonly accepted definition of biological control is:

*The use of living organisms to suppress the population of a specific pest organism, making it less abundant or less damaging than it would otherwise be [1]***.**

The organisms used to feed on, parasitize, or otherwise interfere with targeted pests are called as the *biocontrol agents*. **Table 1** below summarizes some of the different types of biological control agents.

Though the biological agents controls the pest populations with the use of natural predators and minimizes their impact on economic and environmental practices, however, this control method can offer a few distinct advantages as well as disadvantages.

#### **1.2 Advantageous and disadvantages of biological control over chemical/other control methods**

Entomologists consider biological control as an option when the widespread and repetitive usage of chemicals develops resistance in insects. It is a great deal of concern in the recent years.

Extensive application of chemicals is the primary reason for undesirable ecological side effects. Agrochemicals cause many environmental adverse consequences. They may contaminate the groundwater; some may enter the food-chains as a consequence producing a threat to the health of human and other organisms. Besides, the spraying of pesticides is also unsafe for the user. Frequent use of chemical causes inefficacy and is an important part of agricultural enterprise cost [3, 4].

Besides the known adverse consequences of pesticides use, it is not possible to uproot chemicals from the pest management. However, pest mortality caused by chemicals should be added/included to natural causes of death rather than considering the death as substitutive. And here the importance of natural enemies becomes more comprehensible, as the eradication of one pest species could lead to enormous increase in other pest numbers [4].

Therefore, the increasing concern of adversities associated with pesticide use is resulting in a more environmental friendly and sustainable agriculture. Several acceptable regulations are imposed with chemical restrictions or bans, especially in the developed nations. And here natural control method is gaining more attention for pest management at the better prices in market. Such factors hopefully create a favorable condition for the widespread of biological control methods [5].

### *1.2.1 Advantages*

Biological control has several advantages as a pest control method, especially when it is compared with insecticides. The most pivot benefit is that such control methods are environmental friendly and do not add any pollutant into the environment. Kok [6] stated that biological control method may be applied whenever required as it does not pollute the environment.

Another most important advantage of this method is its selectivity i.e., specific pest target strategy. Unlike the chemical/other control method, this method controls the pest meant to target and do not harm the other species or plant. Therefore, danger of damage to non target plant species is restricted. Weeden and Shelton [7] have confirmed that this natural control method do not arise any new complication, like conventional pesticides. However, the side effects may not be totally excluded, though it rarely appears [8]. When discussing the balance of agricultural ecosystems, selectivity plays a vital role because a great damage to non target species can lead to the restriction of natural enemies' populations. Once the natural enemies are introduced into the environment, they reduce the target pest population and sustain their own population as well. Therefore, after initial introduction very little effort is required to keep the system in balance. How successfully a Biological control agent (BCA) can be deployed in an agricultural ecosystem, so as not to damage non target pests, depends on appropriate host specificity tests which determine the potential host range [6].

Another interesting advantage of biological control method is the ability to selfperpetuate. According to Kok (1999), biological control agents will increase in their number and spread. They are self-propagating, dispersing, and self-perpetuating too. This becomes important in relation to the economic feasibility of biological control [9].

An important advantage of biological control method is that the pest is unable or very slow to develop resistance [7]. It is generally not possible for a target pest to develop mechanisms of defense when attacked by a natural enemy [10]. Some examples of defense mechanisms that could develop by pests are escape behavior and repellent chemicals. However, as Van Emden [8] states that "*we know of no cases where previously successful biological control has failed because of selection for resistance*".

The adopted and established biological control methods in a specific area can be kept in a place for longer time than the chemical or other control methods which require repetitive application [6]. Hence, biological control methods are also cost effective as they are needed to be applied only once. The effectiveness of biological control methods is higher than the other control methods and is based on self-perpetuation and self-propagation as mentioned earlier. A small number of biocontrol agents can grow to very high densities and provide continuous control of a pest over a large area. When the cost of deployment of biological control agent is considered in contrast to pesticide applications, biological control is generally less expensive than the chemical control [11]. The financial benefit of biological control is greatest in cases when there is no other option. Another interesting point regarding the cost efficiency of this method is that the yield benefit of biological control is probably less than yield achieved by agrochemicals, but the primary cost of biological control agent is generally lower than chemical pesticides [9].

#### *1.2.2 Disadvantages*

There are several cases where we also find the breakdown of successfully implemented biological control programmes. The story of the Cane toad introduction in Australia and *Harmonia axyridis* introduced across continental Europe as a biological control agent is the best example. In 1935 canes toads were introduced in Australia as a biological control method against the Greyback cane beetle damaging the sugarcane crops. However, the management went horribly wrong because the life history and ecology of cane toads were not fully considered before its introduction and the cane toads today have become an invasive pest in Australia. Similarly, *H. axyridis* (Coleoptera: Coccinellidae), the harlequin ladybird, was from Sible Hedingham, Essex, England, in 2004 [12] and introduced in the areas of continental Europe as a biological control agent against aphids. The individuals dispersed and became invasive from Europe to Britain due to their excellent dispersal abilities as well as some anthropogenic activities also [13, 14].

Therefore, there are also serious disadvantages that restrict the popularity and use of biological control agents to the growers promoting the chemical use. The most important disadvantage is the probability of revenue stability. Reichelderfer [9] well mentioned that the biological control agents are highly proned to environmental conditions rather than the chemical control. As a consequence the pest population is highly fluctuated. And this is a challenge for the growers in relation to the product quality, to the crop yield and obviously to the price of product on market. Moreover, if the annual harvest of a crop is not stable, it will affect grower's income stability.

Another important disadvantage is the incompatibility with conventional pesticides by the growers. Growers are characterized by lack of patience and chemical control is one of the quick fix to any pest population [6]. Hence, the growers prefer the potent pesticides rather than the biological control method which is a slow process and requires lot of time and patience producing long term effect. Van Emden [8] states the limitation of biological control over subsequent use of pesticides, "*where biological control agents are being used against one pest, it is clearly difficult to continue using insecticides against other pests on the same crop or other disease vectors in the same area. This may make the use of biological control impossible*". The slow action of biological control lacks the immediacy of chemical control [6]. This method only reduces the number of pest population; it does not completely wipe out the pest as the chemical control methods. The pests are present in intolerable populations. And the pesticides cannot be used as it will destroy the biological control system. Therefore, shifting to the use of biological control from chemical control is unattractive for growers [8].

Due to the reliability of natural enemies on environmental conditions biological control is often unpredictable. It is well reported in the biological control of whitefly in glasshouses, that a sudden change in weather or a period of extreme hot or cold may lead to a breakdown of the system" [8]. The introduction of natural enemies in a new environment needs to carry out extensive research work to achieve the desirable results against climatic constraints.

Another disadvantage of biological control is that it does not exterminate the pest. As Weeden and Shelton [7] points out that: *the general aim of biological control is to depress the pest population below the Economic Injury Level (EIL): i.e., where the costs of the control measures start to exceed those of the extra revenue.* When this method is used to control the pests in fresh fruits and vegetable, where certain quality standards are demanded by the consumers, the incomplete pest control is not desirable. And damage of product appearance is, therefore, not acceptable by the growers [9].

Selectivity is a major advantage of biological control method, however, it could also be disadvantageous. Since, natural enemies are species specific, the other

#### *Biological Control of Agricultural Insect Pests DOI: http://dx.doi.org/10.5772/intechopen.104464*

pests which are not affected could cause damage, so that the benefit of bio control technique could be extremely eliminated. Reichelderfer [9] has stated that *when several insect species of the same general type are potential pests of the crop, the economic efficiency of biological control technique is extremely restricted.*

Though this method of control is cost effective, a lot is expensed for its successful implementation in the environmental system. Butt [3] mentions that the lack of infrastructure which facilitates transfer of new technologies and research knowledge to the growers is a major inhibitor factor to its commercial perspective. It is not easy and sometimes expensive too for implementing biological control in field because it requires high qualified scientific staff [7]. The growers generally choose the easy applications of pesticides. There is also relatively less investment in biological control research in compare with chemical pesticides.

Variability in the production batches is also one of the significant disadvantage. "The variation and changes in behaviour of natural enemies that can be caused by rearing conditions are manifold" [15]. This variation arises due to lack of appropriate rearing procedures and often leads to incompatibility. The application of appropriate rearing procedures and the production of high quality biological control agents ultimately increase the cost production of natural enemies. Due to this cause, quality measures in mass rearing are often not applied by companies and consequently production of good quality natural enemies becomes challenging [15].

Even though the biological control method is environmentally safe as it provides less risk of residues in food chain, there are risks associated with disruption of biological control agents in the natural food chain. Kok [6] has reported that "*biological control is most suited for exotic pest that are not closely related to indigenous beneficial species*". Thus, the natural enemies must be exotic species too. Lenteren [15] has mentioned few negative effects for the import of natural enemies and many countries deal with risk issues concerning a release of a new natural enemy. However, none of the biological control agent alone provides a completely satisfactory solution to crop pest control problem [4].

**Table 2** summarizes the advantages and disadvantages of biological control over chemical/other control methods:

The use of biological agents to control pest population has long history. Biological control has been in practice since ancient times, however, they were not scientifically validated. During ancient times, Chinese, observed that ants were effective predators of many citrus pests. They multiplied and increased the populations of ants and took their nests from surrounding habitats and placed them into


#### **Table 2.**

*Advantages and disadvantages of biological control over chemical/other control methods.*

their orchards. Thus, the use of natural enemies to reduce the impacts of pests is just a modern adaptation of the original ideas from the history. In this chapter we will discuss the theories of biological control and examine their approaches and applications in the modern pest management.
